The present invention relates generally to a grate bar for use in a solid fuel burning furnace apparatus having a traveling grate bar mechanism, and more particularly to an improved grate bar having unique, localized hard wear surfaces for eliminating premature wear and extending the useful life of the grate bar.
Grate bars for use in a solid-fuel-burning furnace apparatus having a traveling grate bar mechanism are designed to operate in a very severe environment. For example, the grate bars must be capable of withstanding the extremely elevated temperatures found in the combustion chamber of the furnace apparatus. At the same time, the grate bars must be able to resist significant shock loads, such as the shock resulting from objects falling onto the grate bars from high up in the furnace, like slag or metallic and concrete items that can be included with refuse fuels. Thus, grate bars must be designed not only to be heat resistant but also to be tough and ductile. Consequently, grate bars are typically cast from materials such as ductile iron, cast iron or stainless steel, they have a hardness value on the order of about 220 Brinell and they are costly components of the traveling grate bar mechanism.
However, in certain solid-fuel-burning furnace apparatus, such as those that burn RDF or other refuse fuels, the grate bars of the traveling grate bar mechanism have been known to experience excessive wear which reduces their expected operating life and makes it necessary to replace them prematurely and at a significant cost. It has been discovered that often times a portion of the fuel fed into the furnace apparatus consists of non-combustible materials which are very abrasive in nature and are harder than the grate bars. This non-combustible material has been known to eventually become lodged in the traveling grate bar mechanism between the grate bars and the harder support rails along which the grate bars travel. Consequently, the harder, abrasive, non-combustible material causes the softer and more ductile grate bars to wear prematurely.
In addition, the potential for such an excessive wear problem could exist in a coal-fuel-burning furnace apparatus where there are high percentages of ash and the grate bars travel too rapidly through the combustion chamber of the furnace. Situations such as the one just described could be present in the coal-fuel-burning furnace applications in foreign countries as well as when lower grade coal supplies are used as fuel in the United States.
It is believed that increasing the hardness of the portions of the grate bars that travel along the support rails would alleviate the excessive wear described above and, thus, would eliminate the costs associated with prematurely replacing the grate bars. However, attempts to accomplish this objective by the method of heat treatment are considered impractical. One reason for this conclusion is that the ductile, heat resistant materials from which the grate bars are formed are not well-suited for heat treatment. This is especially true of stainless steels. Another reason is that any increase in the hardness of the grate bars achieved by the method of heat treatment could be lost in the high-temperature operating environment of the furnace apparatus. Still a third reason is that an attempt to increase the hardness of the grate bar by the method of heat treatment could cause a corresponding decrease in the ductility of the grate bar and, consequently, could cause the grate bar to be unacceptably brittle.
The extended life grate bar for use in a solid fuel burning furnace apparatus having a traveling grate bar mechanism of the present invention, however, achieves the result of increasing the hardness of the grate bar while, at the same time, overcoming the practical limitations of heat treatment. The present invention is a grate bar having hard wear pad inserts that are integrally disposed within the grate bar. The wear pad inserts can be fabricated from any suitable extra hard high-wear material, such as a hard nickel-steel alloy material, for example, the material well-known by the tradename "Ni-Hard." Further, it has been discovered that the wear pad inserts can be "cast in" the grate bar at the time the grate bar is formed.
The extended life grate bar of the present invention eliminates the excessive wear known to occur in conventional grate bars. An additional advantage of the present invention is that it increases the reliability of the traveling grate bar mechanism and eliminates expenses associated with the replacement of prematurely worn grate bars, such as lost production time and replacement part costs. A further advantage of the present invention is that it may be easily incorporated into the design of a conventional grate bar, thereby minimizing any costs associated with achieving the advantages of the present invention.
Other advantages and features of the present invention will become apparent to one skilled in the art in light of the following description and claims, taken in conjunction with the accompanying drawings.